The production of petroleum or natural gas requires a well that penetrates at least one petroleum or gas containing subterranean formation. In doing so, it is not unusual for such wells to penetrate one or more petroleum or gas containing subterranean formations which also contain unconsolidated mineral particles, such as sand or gravel. The removal of petroleum, gas, water and other production fluids from such a formation during the production process may cause the unconsolidated mineral particles to enter the well along with the production fluids. Such occurrences often lead to a number of difficult and expensive problems.
One problem encountered in some circumstance is that a well will "sand up", that is to say, the downhole portion of the well fills with sand. Because the downhole portion of the well is sanded-up, further production of fluid from the formation becomes difficult or impossible. Another problem that may be encountered is when sand is produced along with the production fluid. The continuous inclusion of sand in the production fluid causes accelerated wear in the pumps and associated mechanisms utilized during the pumping of the production fluids from the well due to the abrasive affect of the mineral particles. Yet another problem that may be encountered in such wells is the gradual removal of mineral particles from the formation around the downhole well area during the pumping of production fluid. Over time this gradual removal of mineral particles causes a cavity to form in the subterranean formation which eventually collapses destroying the well.
The above noted problems and others caused by the inclusion of mineral particles in production fluids should be well known to one skilled in the art. Methods have been devised and applied to petroleum wells in order to reduce or eliminate the production of mineral particles during the course of petroleum production. Such methods include the use of downhole particle screens and filters, gravel packing methods and treatment of the formation with various polymerizable resin compositions which consolidate the mineral particles into a fluid permeable mass.
In addition to the problems resulting from the production of naturally occurring mineral particles, it is sometimes desired to fracture the subterranean formation to increase the volume of production from the well. Hydraulic fracturing of the subterranean formation takes place when hydraulic pressure applied from the surface, causes the formation to crack or fracture. In order to keep the fracture open, propant materials such as sand, glass beads, ceramics, polymer beads and other such materials known in the art are pumped into the open fractures. Upon the start of production, propant material may be dislodged due to the flow of production fluids. The inclusion of propant materials in the production fluids act in a similar manner as naturally occurring sand. That is to say the presence of propant material in the production fluids results in the premature wear of the down hole pump and other components and can result in the "sanding in" of the well.
Another area of concern encountered during petroleum production occurs when a well is in fluid communication with a subterranean formation that includes one or more petroleum producing formations and one or more water producing formations. Production of petroleum from such a well can result in the production of both water and petroleum. Because the viscosity of petroleum is typically higher than water, a large volume of water may be produced along with the petroleum. The amount of water contained in the production fluids often referred to as the "water-cut." Wells with a high water-cut are difficult and expensive to operate because a substantial amount of the production volume lost due to the presence of water. In addition, processes for separating the petroleum from the water and disposal of the water in an environmentally sound manner must be carried out on the surface which increases both capital and operating costs. Thus it is desirable to minimize the water-cut in the production fluid pumped to the surface by controlling the flow of water into the well from the water producing formations. Methods which have been developed to accomplish this goal include downhole separation techniques and methods of controlling the water flow by sealing off the source of water with a thermoplastic resin as well as other methods which should be known to one skilled in the art.
Yet a third problem encountered by the petroleum industry occurs when an unproductive well is to be abandoned. Before abandonment, a well needs to be effectively and permanently plugged to prevent the migration fluids from one or more subterranean formation to another subterranean formation. The plugging of a petroleum well is especially important because the well may penetrate formations containing fresh water that may be used for drinking or other purposes. The long term durability and compressive strength of the materials used to plug wells in preparation for abandonment is of great concern because of the potential for the contamination of the fresh water formation by salt water or petroleum formations which the well may also penetrate. One method of preventing such migrations is to plug the well with a thermoplastic resin. Typically such plugs include materials to prevent shrinkage or fillers to minimize the amount of thermoplastic resin that is used. If the plug is to be long lasting, it should be able to withstand the conditions encountered downhole for long periods of time.
One manner of overcoming the above problems is to use thermosetting resins to consolidate the unconsolidated mineral particles or to control the production of water from an intervening formation or to permanently plug a well prior to abandonment. One of the more successful thermosetting resins used for these purposes is furfuryl alcohol oligomer resin. Furfuryl alcohol oligomer resin is readily polymerized to form a polymer that is durable in the presence of high temperatures and caustic substances. Initiation of the polymerization reaction of furfuryl alcohol oligomer resin is temperature dependent and the reaction requires the presence of an acid catalyst. However, care needs to be taken when using such furfuryl alcohol resins in subterranean wells for these purposes due to the rapid exothermic nature of the polymerization reaction. It has been reported in the art that uncontrolled polymerization reactions of furfuryl alcohol resin in petroleum wells has generated enough heat to cause the subsurface explosion of the well.
In a relevant U.S. Pat. No. 5,285,849 and others noted therein, toluene sulfonic acid is disclosed as being a useful catalyst that gives a controlled autopolymerization reaction. Despite the success of this furfuryl alcohol oligomer resin system, laboratory testing and field use have identified aspects which need improvement:
1. At formation temperatures below 49.degree. C. (120 F..degree.), and at formation temperatures above (270 F..degree.), the polymerization time for furfuryl alcohol oligomer resin becomes unpredictable using toluene sulfonic acid as the catalyst. As a result of this unpredictability, a loss in production time occurs. PA1 2. The inclusion of a super-slurper polymer to prevent shrinkage or expansion of the cured resin or the inclusion of filler materials to increase volume of a plug material causes unpredictable and excessively long curing times when toluene sulfonic acid is used as the polymerization catalyst. PA1 3. Due to the downhole environment, increased adhesion of the cured furfuryl resin to the surface of the mineral particles is desired. An increase in particle adhesion is readily reflected by an increase the compressive strength and results in an increase in the durability of the consolidated particle mass.